Traeling wave amplifier tube



Sept. 16, 1952 R. wALLAUscHEK TRAVELING WAVE AMPLIFIER TUBE Filed April 13, 1948 nul,"

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RICHARD umuscnm.

Sept i6 '1952 R. wALLAUscHl-:K 2,611,101

TRAVELING WAVE AMPLIFIER TUBE Filed April 13, 1948 A 2 sl'lEETS-Sl-IEET 2 RICHARD ALLAUSGM@ l 112i. A

Patented Sept. 16, 1952 TRAVELING WAVE AMPLIFIERTUBE Richard Wallauschek, Marly kLe Rc1, France Application April 1s, 194s, serial No. 20,667 Y In France April 15, 1947 n 6 Claims. v(Cl. 31a-3l l This invention relates to travelling wave ampliner tubes and more particularly to a delay or lag line for use in such an amplier.

The use of 'so-called travelling wave amplifiers is common in the art of ultra-high frequency apparauts and vsuch amplifiers are basically characterized in that they are the 'seat of an interaction between an electromagnetic wave and an electron beam both propagated at velocities which differ little from each other and in that the electric field of said wave vpresents a component directed conformably tothe electron beam. Such an arrangement provokes in certain conditions a progressive modulation of the beams density and an amplication of the wave during its propagation. An essential part of said travelling wave amplier is a delaying line in which Vthe wave to be amplified Vpropagates at a velocity which is notably lower than the velocity of light. Velocity c o'f the beams electrons is always Ylower than the propagation velocity of Afree waves in a vacuum; furthermore, it is limited by the Aneed not to set in action continuous accelerating tensions that are too high. Ifoo vhigh 'values cannot, therefore, ybe considered 'for 'D and to generate waves propagating at approximately 'the velocity o very effective delaying lines must be devised.

The delaying lines to be .placed into action must have very constant properties for a good portion of 'their length at the riskof 'introducing useless reflections which would lower the ampliflers gains'. i

' Thus the invention 'relates to travelling Wave ampliiier tubes in which an electron 'stream and electromagnetic waves circulate and react on each other. As indicated rabove it is necessary to strongly retard the travel 'of the electromagnetic waves becausethey proceed in a straight line at the speed oi light while the electrons practically cannottravelat such speed. It is however necessary that their speed be o'f yabout 'the same order.

In order to delay the travel of the electromagnetic waves, means for forcing them t'o follow a helical path may be employed, and this provides -for some retardation. However, in such an arrangement, in order to effect a sufficiently great retardation, the windings of the helix must be .crowded very close together and this creates certain diliculties, in that, .from the mechanical point of view, it is difficult to produce a very narrow-helical conductor with sufficient precision, and that the waves, if the windings are crowded very close together, mayvjump -across the gap between the windings instead of iollowing the helical course.

I have now found that it is possible to build up a helical delaying path for the electromagnetic waves which slows them up considerably, without thel windings being placed close together if the helix issupported by a cylinder of dielectric material. -This material is then instrumental in producing a substantial retardation. The same cylinder may also serve as a carrier for the outer electrode.' f Y This combination provides the following advantages: The helix can be constructed with great precision and since it adheres to the lcylinder, no deformation can take place. The delaying action of the helix is supplemented by the presence of the dielectricmaterial. Finally, it is possible to bring about the maximum amplication of the travelling wave tube by incorporating in the dielectric material conducting substances, in such manner as to regulate the attenuation, i. e. the reduction of power.

`The invention is illustrated, diagrammatically by way of example, in the accompanying drawings, in which: Y Y

Fig. 1 is an axial sectional view of a travelling wave tube embodying 'a 4delay line 'in accordance with the present invention;

Fig. 2 is a part section illustrating the method of manufacture;

Figs. 3a and 3b are fragmentary axial sectional views of another embodiment of the present nvention showing the delay line in two stages of its production; and

Fig. 4 is a perspective view, partly broken away and in section, of another embodiment of the invention.

Referring 'initially to Fig. 1, the numeral l thereon designates a conventional, elongated, evacuated glass envelope. An elec-tron gun, :generally indicated by the numeral 2, of the Aconventional kind employed in cathode ray tube structures, is arranged with its electrodes at Vvone end of the envelope I and includes Va heater 3 and its associated cathode 4, a disc-like, centrally perforated, control grid 5 'and 'focusing and accelerating hollow, cylindrical electrodes 6 4and '1. When the electrodes Yo'f gun 2 are 'energized by a suitable power 'source (not shown), an axialbeam oi electrons Vis generated and directed toward a disc-.shaped collector electrode 8 arranged at the other end -of the elongated envelope l.

In accordance with the broad principles of the present invention, the axial path of travel 9 of the electron Ybeam extends through and .is enclosed within a central bore fl'llextending axially through a cylindrical member I I formed of dielectric material and disposed Within the envelope I.

An internal conductor I 2 is provided in the bore Ill in the form of a helicoidal strip or helix of thin metallic material coated upon the inner surface of the hollow cylindrical member II. An external conductor I3 is provided in the form of a metallic coating covering the entire outer surface of the cylindrical member II. The conductor I3 acts as the outer conductor of a helicoidal co-axial line and also asy a screen for the y electro-magnetic field.

A co-axial input line I2, including an inner conductor I5 and an outer conductor I6, extends into the envelope I at the end of the cylindrical member II adjacent the electron gun 2,'with the inner conductor I 5 being electrically connected tov the adjacent end of the helicoidal internal conductor I2 and with the outer conductor I6 being electrically connected to the adjacent end of the external conductor I3 on the outer surface of cylindrical member II. A similar co-axial output line I?, including an inner conductor I8 and an outer conductor IS, extends through the evacuated envelcpe I at the end of the cylindrical member I I which is adjacent'to the collector electrode 8, with the conductor I8 being electrically connected to the adjacent end of the helicoidal internal conductor I2 and with the conductor IS being electrically connected to the adjacent end of the outer. conductor I3. In addition to acting as parts of the co-a'xial input and output lines I 4 and Il, the conductors I6 and I9 may also serve to position and support the cylindrical member I I within glass envelope i.

In the structural arrangement described above, the cylindrical member II of dielectric material performs three functionsi l. The field of the wave proceeding along the internal helicoidal conductor I2 is considerably delayed by the dielectric; the propagation velocity would be divided by the square root of the dielectric constant if the influence of the central channel were neglected. The increase in delaying efficiency thus obtained permits the use of electron beams of lower velocities which has the advantage of reducing the necessary accelerating tensions.

2. The dielectric acts as a support for the helicoidal conductor I2. This is a support which. for a suitable dielectric, such as one of ceramic material, for example, has a great rigidity; it is not very sensitive to the temperature variations of the helicoidal conductor which means that the delaying lines dimensions during the mounting and the operation thereof is retained with precision.

3. Varying the losses in the dielectric material of the member I2 provides a means of giving the attenuation exactly the value desired for the return Wave existing in the amplifler to be suitably attenuated. The losses of the dielectric can, for instance, be properly proportioned by a suitable addition of scattered conducting substances in the dielectrical substance.

It may be advantageous to progressively vary the attenuation rate along the line so rthat the attenuation is at a maximum at the lines inlet and at a minimum at its outlet; This enables one, for a given total attenuation to dissipate in theline an energy which is weaker than that which wouldbe dissipated for a value ofl the attenuation which lis constant along the line. ThusV Atap 22 of suitable dimensions.

4 the efficiency of the amplier tube can be improved.

The properly chosen dielectric can if desired constitute part of the jacket of the amplifier tube inside of which there is a vacuum.

In the modification illustrated by Fig. 2, the inner surface of the cylindrical member 20 of dielectric material, as well as the outer surface thereof, is initially coated completely with a metallic, electrical conducting material, as shown at 2|. After the coating 2I is applied to the inner surface of member 20, the helicoidal internal conductor is formed by means of a screw This operation, which can eventually be carried out before the last baking of the dielectric, removes from the cylindrical members inner surface all the metal except the metallic ribbon 23 which is to constitute the helicoidal internal conductor. Thus, the completed cylindrical member has .a solid coating i3d on its outer surface, to constitute the external conductor, and a helicoidal strip 0r ribbon 23 onits inner surface, to constitute the internal conductor.

In the modifications illustrated in Figs. 3a and 3b, a helical groove 24 is rst formed in the inner surface of the dielectric cylindrical member 2Go before any metal coating is applied thereto. Then metal is applied, as indicated at 25, to the whole inner surface as schematically shown in Fig. 3a. The inside of the dielectrical member 20a is then reamed or turned so as to leave only the metallic part 26 (Fig. 3b) located at the bottom of the previously excavated groove 24 and forming the helicoidal internal conductor. The external conductcr is again provided by a continuous metallic coating I3b on the outer surface of cylindrical member 20a.

In the arrangement shown in Fig. 4, a helicoidal strip of metal 29 is applied on the outer surface of a dielectrical cylinder 28, the walls of which are relatively thin, and the whole constituted by the cylinder 23 with the strip 29 thereon is inserted into a second dielectric cylinder 30 in which is propagated the outer field of thehelicoidal internal conductor. Such metallization or coating carried out on the outside of a cylinder 28 can be more easily performed. The interior insulating surface of this apparatus can take a negative potential during, the operation of the amplifier tube under the action of the electrons falling on this surface, and this can serve as an additional means of focusing the electron beam.

In the embodiment of Fig. 4, the internal conductor, provided by the helicoidal strip 29, is disposed on cylinder 28, but it is in contact with the internal surface of the outer cylinder 30, while the external conductor is provided by a continuous metallic coating I 3c applied to the outer surface of cylinder 30.

While a number of modifications have been disclosed, it is to be understood that the invention is not limited thereto but is coextensive in scope with the appended claims.

What is claimed is:

1. An ultra high frequency traveling Wave amplifier tube comprising an evacuated envelope having therein an electron gun at one end providing a cylindrical electron beam traveling with a predetermined velocity, a collector electrode located at the opposite end to receive said electron beam, a cylindrical member of dielectric material coaxial with said electron beam, and a low velocity of propagation line having input terminals to receive ultra high frequency energy and output terminals to deliver amplied ultra high frequency energy, said line including a thin conductive coating on the exterior surface of said cylindrical member to provide an external conductor. and a thin conductive coating contacting the interior surfa-ce of said cylindrical member and in the form of a helix to provide an internal conductor, the helical form of said internal conductor having a pitch operative to produce a propagation velocity of the electromagnetic wave traveling along said line substantially equal to said predetermined Velocity of the electron beam.

2. An ultra high frequency traveling wave amplifier tube according to claim 1; wherein said cylindrical member is formed of a ceramic material.

3. An ultra high frequency traveling wave amplier tube according to claim 1; wherein said thin conducting coating in the form of a helix is formed on said interior surface of said cylindrical member.

4. An ultra high frequency traveling wave amplifier tube according to claim 1; further comprising an inner cylindrical member formed of dielectric material and tting closely and coaxially into the rst mentioned cylindrical member, said thin conducting coating in the form of a helix being formed on the external surface of said inner cylindrical member.

5. An ultra high frequency traveling wave ampliiier tube according to claim 1; including conductive particles scattered within the dielectric material of said cylindrical member to provide a predetermined amount of attenuation for the ultra high frequency energy.

6. An ultra high frequency traveling wave t amplifier tube according to'claim 5; wherein the density of said conductive particles decreases in the axial direction of said line to provide maximum attenuation of the input eiid of said line and minimum attenuation at the output end of said line.

RICHARD WALLAUSCHEK.

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS OTHER REFERENCES Article by R. Kompfner, pp. 124-127, Proc. I. R. E., February 1947, (Copy in U. S. Patent Ofice Scientic Library.) 

